While components of modern cellular phones are designed to be very small in size, commercial handsets are not provided in the smallest possible form factor because of human engineering considerations. There is a lower limit, dictated by human physiognomy, on the sizes of components like a screen and a keypad.
Existing cellular phones known in the art are designed as an integrated device for supporting both incoming and outgoing calls.
As the prior art cellular phones are designed to support both incoming and outgoing calls, they have to include a keypad and a display, which consume a lot of “real estate” and are not at all essential for supporting only incoming calls. Configuring these components in an ordinary cellular phone makes it too heavy and large in size to be conveniently worn within a necklace, clipped on a T-shirt, etc.
However, there are many situations where a user needs to immediately respond to some incoming calls, but does not need to initiate outgoing calls with the same urgency. Such situations are typical to professionals on duty (such as medical doctors, police officers etc.) and to anyone while engaged in sporting activities (such as jogging, riding bicycles, etc.).
Users require different needs and expectations when handling incoming calls and outgoing calls. Some of the major differences are highlighted in the following table:
AspectIncoming callOutgoing callRequired response time to a stimulus1-3 secondsMinutesNeed to see a screenNoYesNeed to divert a call to another partyYesNoNumber of clicks for the operation  1ManyAbility to batch for later executionNoYesNeed to be reminded to executeNoYesCost of operation to user~0SomeNeed background informationNoYesNeed to repeat on failure (busy)NoYes
Hence, there is a major difference between the minimum sizes of a cellular phone designed to support incoming calls only, and a cellular phone designed to support both incoming and outgoing calls.
A known in the art technique is a pager, i.e. an electronic device used to contact people via a paging network. A pager pre-dates mobile phone technology, but similarly uses radio transmissions to communicate between a control/call center and a recipient. Pager models in use today use digital messages, first numeric and later alphanumeric, to provide the recipient with more information. Such pagers include the ability to send messages in a two-way fashion and even include the ability to send an email. This is known as two-way paging.
However, the pager devices used today require the paged party (i.e. recipient) to phone the control/call centre in order to collect the message either from a cellular telephony network an operator or a voice-mail device.
Another existing technique for small size telephone device is to use a Bluetooth transponder (i.e. a phone that is based on Bluetooth technology) having a base unit associating to one or more handsets.
However, such an ordinary sized phone Bluetooth transponder is limited to supporting a base unit located only few meters away and can not serve the need described above.
Therefore, it would be desirable to provide a cellular phone having a minimum size foreground unit and a background unit, physically separated from the foreground unit and in local communication with the foreground unit, wherein said foreground unit supports incoming calls independently of the background unit, and wherein the foreground unit and the background unit cooperate to support outgoing calls.